Thoracoabdominal Aortic Challenges
Joseph S. Coselli, MD
Baylor College of Medicine/The Methodist Hospital
Houston, Texas
 
Thoracoabdominal aortic aneurysms are those aneurysms that involve both the descending thoracic aorta and varying portions of the abdominal aorta. Despite continued advances in medical therapy, conventional resection and graft replacement remains the treatment of choice for these more extensive aortic aneurysms. These lesions continue to remain a formidable challenge to the vascular surgeon as a consequence of variable pathology, extensive lengths of aortic involvement, and the operative procedures required for treatment. There has been a marked improvement in the overall survival rate and a lowering in the incidence of significant morbidity.

The most devastating, and as yet unsolved, postoperative complication following thoracoabdominal aortic aneurysm resection is the development of paraplegia or paraparesis resulting from spinal cord ischemia. As yet, no reproducible and reliable method for protecting the spinal cord from ischemia during aneurysm replacement has been developed.

The bulk of experience in the reported literature has been primarily with the "clamp and sew" technique. Over the last two decades, there has been a resurgence of interest in a wide variety of techniques employed for the purpose of reducing the incidence of spinal cord ischemia. These have included pharmacological intervention directed primarily at reduction of reperfusion injury with steroids, naloxone, papaverine, supraoxide dismutase, allopurinol, calcium channel blockers, barbiturates, perfluorocarbons, and hypoglycemia; bypass techniques, i.e., aortic shunts, femoral-femoral cardiopulmonary bypass, and left heart bypass with centrifugal pumps; and spinal cord protection using moderate hypothermia, profound hypothermia, and epidural cooling.

The retaining of the direct arterial blood supply to the spinal cord has been addressed by attempts to preoperatively identify the blood flow to the anterior spinal artery using preoperative arteriography. The intraoperative identification of the intercostal arteries which supply the spinal cord, by the use of the platinum electrode on the spinal cord and injection of hydrogen ions into the intercostal arteries to delineate the vessels, has received clinical attention. A number of authors have addressed the importance of the reattachment of intercostal arteries at the critical level from T7-T8 to L1-L2. Somatosensory evoked potential (SEP) monitoring is obtained by stimulation of the posterior tibial nerve with a bipolar input channel. A 10 percent increase in latency signals the onset of spinal cord ischemia. Despite its many limitations, including numerous false negatives and false positives, the technique is used by a number of authors to evaluate the intraoperative functional status of the spinal cord. Motor evoked potential (MEP) monitoring allows for direct monitoring of motor track function, providing a real time assessment of the adequacy of spinal cord perfusion. The clinical utility of evoked potential monitoring possibly lies in the ability to evaluate other adjuvant techniques for prevention of spinal cord ischemia.

In addition, cerebrospinal fluid drainage has received substantial clinical attention and is generally targeted at maintaining a cerebrospinal fluid pressure at or below 10mmHg by intermittent drainage. Clinical results have been mixed. There have been as yet no prospective, randomized trials proving its efficacy. Many believe CSF drainage should not be used in patients who are heparinized. A modification with great promise has been the use of an epidural catheter enabling a withdrawal of the cerebrospinal fluid, as well as an infusion of ice (4ºC) normal saline to achieve regional spinal cord hypothermia.

The incidence of paraplegia in patients undergoing thoracoabdominal aortic aneurysm repair ranges from 7 to 33 percent. The major causes of spinal cord injury include the duration and degree of ischemia, failure to re-establish blood flow to the spinal cord after repair, and reperfusion injury of spinal cord. Spinal cord injury has been related to the extent, etiology of aneurysmal disease, patient’s age (greater than 65 years), duration of aortic clamp time (longer than 60 minutes) and presence of aortic dissection. Anatomically, blood supply to the spinal cord is segmental and variable. The main arterial supply of the spinal cord arises from the T5 to T8 segments in 15 percent, T9 to T12 in 75 percent, L1 to L2 in 10 percent, L3 in 1.4 percent and L4 to L5 in 0.2 percent. Consequently, T9 to T12 intercostal arteries are important to maintain perfusion of the spinal cord. Frequencies of postoperative combined paraparesis and paraplegia for nondissecting TAAA extents I, II, III, and IV are 12 percent, 27 percent, 4.6 percent, and 3 percent, respectively. In the presence of aortic dissection, these ratios are 21 percent, 33 percent, 13 percent and 11 percent, respectively. Despite previous reports that show a significant association between the presence of aortic dissection and postoperative paraplegia/paraparesis, most current reports confirm that dissection is no longer a variable associated with the development of postoperative paraplegia/paraparesis.

The average operative mortality risk for patients undergoing thoracoabdominal aortic surgery is 11 percent. The mortality rate for emergency procedures is as much as seven times higher than that for elective procedures. The causes of death in the perioperative period are preoperative aneurysm rupture, low cardiac output, renal failure, pulmonary insufficiency and myocardial infarction. The determinants of in-hospital mortality are renal failure, pulmonary complications and postoperative paraplegia. The actuarial survival estimates for discharged patients were 70-79 percent and 40-49 percent at 5 and 10 years, respectively. Hypertension and preoperative congestive heart failure were independent predictors of late mortality.

Dr. Crawford has reported the largest series to date of patients submitted to operation for thoracoabdominal aortic aneurysms, of which 1386/1509 (92 percent) were early survivors. Preoperative variables predictive of early death were advanced age, rupture and preexisting cardiac, pulmonary and renal disease. The reoperation rate for complications was 2.4 percent. The significant predictors of paraplegia or paraparesis were total aortic clamp time, extent of aorta repaired, aortic rupture, patient age, proximal aortic aneurysm, and history of renal dysfunction. The 5-year survival rate of patients with nondissecting aneurysms was about 6 percent greater than those with dissection due to the high frequency of aortic rupture in those with dissecting aneurysms. The estimated long-term survival rate was 59 ± 3 percent at 5 years and 32 ± 6 percent at 10 years. Risk factors predicting late death were advanced age, rupture, renal dysfunction, extent of disease, and dissection.

The current results of the author’s experience with thoracoabdominal aortic aneurysm repair are listed in the table that follows:
 
 

Extent 
# of pts 
30 day 
survival 
In-hospital 
survival 
Paraplegia/ 
paraparesis 
Renal Failure 
Bleeding 
I
400
380
(95.0%)
370
(92.5%)
16
(4.0%)
11
(2.8%)
6
(1.5%)
II
343
325
(94.8%)
314
(91.5%)
28 
(8.2%)
32 
(9.3%)
13 
(3.8%)
III
184
175
(95.1%)
175 
(95.1%)
7
(3.8%)
11
(6.0%)
2 
(1.1%)
IV
213
206
(96.7%)
201
(94.4%)
3
(1.4%)
16
(7.5%)
3
(1.4%)
Total
1140
1086
(95.3%)
1060
(93.0%)
54
(4.7%)
70
(6.1%)
24
(2.1%)
 

References

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